There is a lot of subjectivity with the MVP - especially when the field is fairly close. This year is also fairly close - as I noted, Betts winning is not any sort of robbery. (the example I always bring up for an actual robbery is Mo Vaughn in 1995)
Ortiz would be good narrative - which is fine - but he has played less than his compatriots, and since his contribution is entirely offensive - he has to be a lot better than other guys on that dimension, and he isn't.
The voting for the mvp in 1931 was of course when tools to measure actual value did not exist - you had to look at your classic roto stats and take the plunge.
For me, it's Trout vs Betts. Given the tools to measure value, those two have delivered significantly more value than anybody else - so to me they are the most valuable players this season. It really comes down to whether Betts' defense is enough to offset the sheer number of outs he made compared to Trout.
In real life, I expect Betts to win it.